40 research outputs found
Collective-coordinate analysis of inhomogeneous nonlinear Klein-Gordon field theory
Two different sets of collective-coordinate equations for solitary solutions
of Nonlinear Klein-Gordon (NKG) model is introduced. The collective-coordinate
equations are derived using different approaches for adding the inhomogeneities
as exrernal potentials to the soliton equation of motion. Interaction of the
NKG field with a local inhomogeneity like a delta function potential wall and
also delta function potential well is investigated using the presented
collective-coordinate equations and the results of two different models are
compared. Most of the characters of the interaction are derived analytically.
Analytical results are also compared with the results of numerical simulations.Comment: 16 pages, 8 figures. Accepted for publication in Volume 43 of the
Brazilian Journal of Physic
Vortices in polariton OPO superfluids
This chapter reviews the occurrence of quantised vortices in polariton
fluids, primarily when polaritons are driven in the optical parametric
oscillator (OPO) regime. We first review the OPO physics, together with both
its analytical and numerical modelling, the latter being necessary for the
description of finite size systems. Pattern formation is typical in systems
driven away from equilibrium. Similarly, we find that uniform OPO solutions can
be unstable to the spontaneous formation of quantised vortices. However,
metastable vortices can only be injected externally into an otherwise stable
symmetric state, and their persistence is due to the OPO superfluid properties.
We discuss how the currents charactering an OPO play a crucial role in the
occurrence and dynamics of both metastable and spontaneous vortices.Comment: 40 pages, 16 figure
Ultra-low-power hybrid light-matter solitons.
New functionalities in nonlinear optics will require systems with giant optical nonlinearity as well as compatibility with photonic circuit fabrication techniques. Here we introduce a platform based on strong light-matter coupling between waveguide photons and quantum-well excitons. On a sub-millimetre length scale we generate picosecond bright temporal solitons at a pulse energy of only 0.5 pJ. From this we deduce a nonlinear refractive index three orders of magnitude larger than in any other ultrafast system. We study both temporal and spatio-temporal nonlinear effects and observe dark-bright spatio-temporal polariton solitons. Theoretical modelling of soliton formation in the strongly coupled system confirms the experimental observations. These results show the promise of our system as a high speed, low power, integrated platform for physics and devices based on strong interactions between photons
Rogue events in the group velocity horizon
The concept of rogue waves arises from a mysterious and potentially calamitous phenomenon of oceanic surfaces. There is mounting evidence that they are actually commonplace in a variety of different physical settings. A set of defining criteria has been advanced; this set is of great generality and therefore applicable to a wide class of systems. The question arises naturally whether there are generic mechanisms responsible for extreme events in different systems. Here we argue that under suitable circumstances nonlinear interaction between weak and strong waves results in intermittent giant waves with all the signatures of rogue waves. To obtain these circumstances only a few basic conditions must be met. Then reflection of waves at the so-called group-velocity horizon occurs. The connection between rogue waves and event horizons, seemingly unrelated physical phenomena, is identified as a feature common in many different physical systems